This invention relates to an improved process for production of polyamide yarns and to an improved polyamide yarn for use in apparel applications.
More particularly the invention relates to an improved process for spinning polyamide yarns using a polymer flake (also called polymer chips or granulate) remelting process. In many prior art polymer flake remelt processes a solid phase polymerizer is used to build the polymer relative viscosity (RV) to a higher level for spinning yarns of higher tenacity and toughness. Yarn quality is directly affected by its tenacity and toughness providing a product which is more widely acceptable in variety of apparel applications.
In U.S. Pat. No. 4,952,345; Rao et al. disclose a control method to use a solid phase polymerizer or SPP (also known as a solid phase polycondensation apparatus) with a polyamide flake remelt process to build the polymer RV in a highly uniform and reproducible way. In U.S. Pat. No. 6,235,390; Schwinn et al. disclose an SPP method and apparatus for building very high RV polyamide polymer filaments by treating the polymer before extrusion with a very low dew point gas. While these prior means to build polymer RV and control the polymer RV to highly uniform value, neither means address the problems problem of process interruptions and fundamental spinning process productivity.
In the manufacture of polyamide yarns, especially nylon 66 yarns, the winding of the yarn is stopped frequently to remove undesirable deposits found around the capillary exit side of the spinneret plate. If not removed these deposits build up to a thickness of a “few millimeters (per) week” according to Fourné (Synthetic Fibers, Chapter 4, page 359, C. Hanser Publishers, Munich 1998.) Such deposits cause the filaments to bend or “knee.” Bending of a majority of the filaments, if not remedied, ultimately leads to filaments breaks, yarn defects or unscheduled process interruptions. Increasing numbers of process interruptions especially, lead to the yarn spinning process becoming less efficient.
The problem of bent filaments tends to increase with increasing filament delusterant content. Titanium dioxide (TiO2) is a commonly employed delustering pigment. A TiO2 content in the range of 0.03 to about 1.0 per cent by weight in the polyamide polymer provide so-called bright to mid-dull luster in to the filaments. However, a TiO2 content in the range of greater than 1 to about 3 per cent by weight in the polyamide polymer provide dull or “fully dull” luster filaments, desirable in many apparel applications. It is dull luster filament yarns which tend to present more process problems relating to bent filaments.
For a polyamide yarn manufacturing process the cleaning the spinneret plate on the capillary exit face is often referred to in the art as “spinneret wiping.” The time between spinneret wiping events, where each event is necessitated by a build up of the undesirable deposits, is called the wipe cycle time or wipe life. A longer spinneret wipe cycle, the time between cleaning the spinneret face, is more desirable. Means to increase this time needed between spinneret wiping events, the wipe cycle, and in turn the productivity of the a polyamide yarn spinning process; have been sought for many years. There has been a long felt need in the art to provide a polyamide yarn spinning process of higher productivity. While it has been known to those skilled in the art that reducing the numbers of filament breaks, yarn quality defects and unscheduled process interruptions has a direct effect on productivity, means to leverage or remedy such defects have been heretofore elusive.
With this objective in mind, other objects of the invention will be clear from the following description.